Compare list content no matter on order

Hi
I want to compare the content of 2 lists not depended on the
list order and nondestructive on the original lists.

e.g.
listA = list(“a” “b” “c”)
listB = list(“a” “c” “b”)
listC = list(“a” b”)
listD = list(“a” “b” “c” “d”)

listA == listB => t
listA == listC => nil
listA == listD =>nil

I found a very pragmatic approach, but I’m wondering if there
isn’t any better way of implementing such a common task?

Best regards,

 Bernd

 1 procedure(compareListContent(listA listB "ll")
 2     let((returnVal)
 3
 4     if(length(listA) == length(listB) then
 5         foreach(element listA
 6             if(member(element listB) then
 7                 returnVal = t
 8             else
 9                 returnVal = nil
10             ) ;; close if      
11         ) ;; close foreach
12     else
13         returnVal = nil
14     ) ;; close if    
15
16     ) ;; close let
17 ) ;; close proecedure